Both sperm and non-sperm components of the ejaculate play vital roles in postcopulatory sexual selection, and males of many species are able to make adjustments to sperm quality (sperm numbers and velocity) in response to sperm competition risk. The non-sperm component of an ejaculate, the seminal fluid, is molecularly complex, containing a wide range of different classes of molecules that influence both sperm performance and male fertility. However, this non-sperm component of an ejaculate has usually been overlooked in studies of sperm competition. Here we describe series of experiments with chinook salmon (Oncorhynchus tshawytscha), whereby we manipulate male social status to determine whether the changes in sperm quality observed in response to an individual’s social position are the result of alterations in the gametes themselves, seminal fluid, or a combination of the two. Our findings suggest seminal fluid differentially affects sperm performance according to male social status, highlighting the importance of the seminal fluid on male reproductive performance and fitness.